Prestressed bearing for electrical machines

ABSTRACT

The present invention relates to an electrical machine  1,  in particular an electric motor, with a housing  2  and covers  3, 4  that close the housing  2  and contain bearings  7, 8  that rotatably support a rotor  5.  According to the present invention, spring elements  7.3, 8.3  are provided that act upon at least one bearing shell  7.1, 7.2, 8.1, 8.2  each of bearings  7, 8  with a compression force acting in the axial direction, whereby the mounting of the bearing shell  7.1, 7.2, 8.1, 8.2  that is acted upon by one of the spring elements  7.3, 8.3  is configured as a sliding fit.

TECHNICAL AREA

The present invention refers to an electrical machine, in particular anelectric motor, according to the definition of the species of claim 1.

BACKGROUND INFORMATION

The rotatably supported parts of an electrical machine, such as therotor of an electric motor, are typically supported in ball bearings.When the direction of rotation of the rotor changes, bearings of thistype can produce noises that are disruptive and negatively affectcomfort. The disruptive noises are produced because the balls in theball bearing start to travel when the direction of rotation of the rotorchanges and strike the other race shoulder of the bearing shell of theball bearing. The noise is amplified further by the fact that rotoroscillations occur when the direction of rotation of the rotor changes,the rotor oscillations then being transferred to the housing of theelectrical machine.

ADVANTAGES OF THE INVENTION

The present invention enables substantially play-free support ofrotatably supported machine elements, such as the rotor of an electricmotor. Since there is practically no play in the axial direction, rotoroscillations-which could cause disruptive noises to be produced-do notoccur even when the direction of rotation and the axial force change.Due to the substantially constant orientation of the rotor relative tothe bearings, the balls in the bearing are successfully prevented fromtraveling and striking the race shoulder of the bearing shell, even whenthe direction of the axial force on the rotor suddenly changes. As aresult, disruptive noises are prevented. Furthermore, the presentinvention enables good emergency running properties of the motor, sincethe bearing shells are installed in the housing of the motor with asliding fit. If a bearing jams, the bearing is still able to slide inthe housing. Due to the bearing construction designed according to thepresent invention, a very even distribution of the load among the twobearings is obtained. This results in very even wear and, therefore, avery long service life. The components of the bearing are easy tomanufacture and install, which allows the manufacturing costs to benoticeably reduced. Finally, the motor can also be removed easily, toperform wear-induced repairs, for example, without causing any damage.

DRAWING

The present invention is described in greater detail below withreference to the drawing.

FIG. 1 shows an electrical machine, in particular an electric motor, ina longitudinal sectional view,

FIG. 2 shows the schematic illustration of a rotor supported in bearingsin a first exemplary embodiment of the present invention,

FIG. 3 shows the schematic illustration of a rotor supported in bearingsin a second exemplary embodiment of the present invention,

FIG. 4 shows a diagram of the spring force of a spring element of the Abearing as a function of deflection,

FIG. 5 shows a diagram of the spring force of a spring element of the Bbearing as a function of deflection,

FIG. 6 shows a further exemplary embodiment of the present invention,

FIG. 7 shows a simplified exemplary embodiment of the present invention,and

FIG. 8 shows a further simplified exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows an electrical machine 1, in particular an electric motor,in a longitudinal sectional view. A housing 2 that is closed by twocovers 3, 4 encloses a stator 6 and a rotor 5. Rotor 5 is supported intwo bearings, B bearing 7 and A bearing 8, both of which are ballbearings in particular. The endpiece of the shaft of rotor 5 extendingout of housing 2 is configured as a worm 5.1 that meshes with a toothedwheel 5.2.

Further details of the bearing construction designed according to thepresent invention are shown in FIG. 2 and FIG. 3. FIG. 2 shows theschematic depiction of a rotor 5 supported in bearings 7, 8 in a firstexemplary embodiment of the present invention. B lager 7 located incover 3 is composed of an inner bearing shell 7.2 and an outer bearingshell 7.1. Inner bearing shell 7.2 is mounted on the shaft of rotor 5.Outer bearing shell 7.1 is mounted in cover 3 with a sliding fit. Aspring element 7.3 is positioned between outer bearing shell 7.1 andcover 3, and bears against cover 3 and outer bearing shell 7.1. Springelement 7.3 exerts a force on outer bearing shell 7.1 that is directedinwardly in the axial direction. In the diagram in FIG. 5, theretractive force F of spring element 7.3 in newtons is plotted as afunction of deflection s in hundredths of millimeters. The diagram showsthat the strongest retractive force takes effect when rotor 5 isdeflected in the axial direction to the left. Deflection of rotor 5 inthe axial direction to the left is therefore counteracted, and rotor 5is centered in the axial direction to the right. “A” bearing 8 islocated in cover 4 on the right side of rotor 5. “A” bearing 8 includesa lower bearing shell 8.1 and an upper bearing shell 8.2. In turn, lowerbearing shell 8.1 is mounted on the shaft of rotor 5. Upper bearingshell 8.2 of bearing 8 is supported in cover 4 with a sliding fit. Aspring element 8.3 is located between cover 4 and outer bearing shell8.2, the spring element bearing against cover 4 and outer bearing shell8.2. Spring element 8.3 presses rotor 5 in the axial direction to theleft. The diagram in FIG. 4 shows the retractive force F of springelement 8.3 in newtons as a function of deflection s in hundredths ofmillimeters. As shown in the diagram in FIG. 4, the retractive force Fincreases the more rotor 5 moves to the right. The mode of operation ofthe arrangement can be summarized with the following description. Assoon as rotor 5 is deflected to the left, retractive force F of springelement 7.3 increases greatly and forces rotor 5 back to the right.Excessive deflection of rotor 5 to the right, in turn, is offset by theretractive force F of spring element 8.3. The overall result is thatrotor 5 is forced to assume the most stable position of equilibriumpossible between the two bearings 7 and 8. When axial oscillations ofrotor 5 occur, in particular when the direction of rotation changes,spring elements 7.3 and 8.3 further cause balls 7.4 and 8.4 in ballbearings 7, 8 to bear, in a defined manner, against the shoulders oftheir races formed by the bearing shells. As a result, balls 7.4, 8.4are prevented from traveling when the direction of rotation of rotor 5changes, and the noises that would be otherwise produced are prevented.

Further advantageous emergency running properties result from the factthat outer bearing shells 7.1, 8.2 are mounted with a sliding fit. Ifone of the ball bearings 7, 8, or both bearings, become jammed, thesliding-fit arrangement allows outer bearing shells 7.1, 8.2 to continueto rotate, along with rotor 5, in their sliding-fit arrangement incovers 3, 4. The sliding fit arrangement further enables the electricalmachine to be removed directly, to repair worn components, for example,without causing any damage.

A further exemplary embodiment of the present invention is shown in FIG.3. The difference from the exemplary embodiment described previouslywith reference to FIG. 2 is that, in this case, inner bearing shells 7.2and 8.2 are loaded by spring elements 7.3, 8.3. Furthermore, the seatsof inner bearing shells 7.2 and 8.1 on the shaft of rotor 5 areconfigured as sliding fits that, in case of emergency, if bearings 7, 8become jammed, allow emergency running operation. Spring elements 7.3,8.3 bear against a step of rotor 5. A thorough description is notnecessary, since the design is easy to understand. The advantagesdescribed with the first exemplary embodiment are also attainable withthis exemplary embodiment.

A further exemplary embodiment of the present invention is shown in FIG.6. It shows that the design-related means of attaining the object of theinvention for the first exemplary embodiments described can also beadvantageously combined with each other. In this case, for example, withthe B bearing, inner bearing shell 7.2 is loaded by spring element 7.3,while, with the A bearing, outer bearing shell 8.2 is loaded with springelement 8.3. The reverse combination is also possible, of course.

FIG. 7 shows a simplified exemplary embodiment of the present inventionthat can be realized in an economical manner. With this exemplaryembodiment, a spring element 7.3 is provided on only one bearing side ofrotor 5 and, in fact, on B bearing 7, the spring element applyingpressure on outer bearing shell 7.1.

With the further exemplary embodiment-which is also shown in asimplified depiction-according to FIG. 8, a spring element 8.3 is alsoprovided on only one bearing side of rotor 5 and, in fact, on A bearing8 in this case, the spring element applying pressure on inner bearingshell 8.2.

The means of attaining the object of the invention according to thepresent invention was described above in conjunction with an electricalmachine, in particular an electric motor. It is also possible, however,to apply the means of attaining the object of the invention according tothe present invention in any bearing design that requires suppression ofaxial play and, therefore, axial oscillations associated therewith.Reference Numerals 1 Electrical machine 2 Housing 3 Cover 4 Cover 5Rotor 5.1 Worm 5.2 Toothed wheel 6 Stator 7 B bearing 7.1 Outer bearingshell 7.2 Inner bearing shell 7.3 Spring element 7.4 Ball 8 A bearing8.1 Inner bearing shell 8.2 Outer bearing shell 8.3 Spring element 8.4Ball F Retractive force

1. An electrical machine, in particular an electric motor, with ahousing (2) and covers (3, 4) that close the housing (2) and containbearings (7, 8) that rotatably support a rotor (5), wherein, springelements (7.3, 8.3) are provided that act upon at least one bearingshell (7.1, 7.2, 8.1, 8.2) each of bearings (7, 8) with a compressionforce acting in the axial direction, whereby the mounting of the bearingshell (7.1, 7.2, 8.1, 8.2) that is acted upon by one of the springelements (7.3, 8.3) is configured as a sliding fit.
 2. The electricalmachine as recited in claim 1, wherein the bearings (7, 8) are ballbearings.
 3. The electrical machine as recited in claim 1, wherein theinner bearing shells (7.2, 8.1) of the A bearing (8) and the B bearing(7) are mounted on the shaft of the rotor (5), each of the outer bearingshells (7.1, 8.2) of the A bearing (8) and the B bearing (7) areinstalled in the covers (3, 4) with a sliding fit, and one springelement (7.3, 8.3) is provided between each of the covers (3, 4) and theouter bearing shell (7.1, 8.2) that acts on the outer bearing shell(7.1, 8.2) with pressure in the axial direction.
 4. The electricalmachine as recited in claim 1, wherein the outer bearing shells (7.1,8.2) of the A bearing (8) and the B bearing (7) are mounted in thecovers (3, 4), the inner bearing shells (7.2, 8.1) of the A bearing (8)and the B bearing (7) are mounted on the shaft of the rotor (5) with asliding fit, and the inner bearing shells (8.1, 7.2) of the A bearing(8) and the B bearing (7) are acted upon by a spring element (7.3, 8.3)with pressure in the axial direction.
 5. The electrical machine asrecited in claim 1, wherein one spring element (7.3, 8.3) each islocated between the inner bearing shell (7.2, 8.1) and a step located onthe shaft of the rotor (5).
 6. The electrical machine as recited inclaim 1, wherein the outer bearing shell (7.1, 8.2) of the B bearing (7)is mounted in the cover (3), the inner bearing shell (7.2, 8.1) of the Bbearing (7) is mounted on the shaft of the rotor (5) with a sliding fit,the inner bearing shell (7.2, 8.1) is acted upon by a spring element(7.3, 8.3) with pressure in the axial direction, the inner bearing shell(7.2, 8.1) of the B bearing (7) is mounted on the shaft of the rotor (5)with a sliding fit, the inner bearing shell (7.2, 8.1) is acted upon bya spring element (7.3, 8.3) with pressure in the axial direction, theinner bearing shell (8.1) of the A bearing (8) is mounted on the shaftof the rotor (5), the outer bearing shell (8.2) of the A bearing (8) isinstalled in the cover (4) with a sliding fit, and the outer bearingshell (8.2) is acted upon by a spring element (8.3) with pressure in theaxial direction.
 7. The electrical machine as recited in claim 1,wherein the spring forces of the spring elements (7.3, 8.3) are directedtoward each other such that the rotor (5) is stabilized in a centralposition between the bearings (7, 8).
 8. The electrical machine asrecited in claim 1, wherein the retractive force (F) of the springelements (7.3, 8.3) at a distance of s=150*0.01 cm is between 2500 and4000 newtons, preferably 3200 N.